Leases - Additional Information (Details) - USD ($) $ in Millions	1 Months Ended			3 Months Ended
	Oct. 31, 2018	Feb. 28, 2018	Jan. 31, 2010	Mar. 31, 2019	Mar. 31, 2018
Lessee Lease Description [Line Items]
Weighted average remaining lease term				6 years 8 months 12 days
Weighted average discount rate used to determine the right-of-use assets and corresponding operating lease liabilities				6.40%
Rent expense				$ 0.1	$ 0.1
Malvern, Pennsylvania
Lessee Lease Description [Line Items]
Lease commencement date			Mar. 31, 2010
Lease extended expiration date		Sep. 30, 2023	Jul. 31, 2018
Additional period option to extend the lease		3 years
Lessee, operating lease, option to extend description				amended to extend its term to July 31, 2018 and again to September 30, 2023, with an option to extend the lease for an additional three years.
Lessee, operating lease, existence of option to extend [true false]				true
San Diego, California
Lessee Lease Description [Line Items]
Lease expiration date	Oct. 31, 2022